1. Field of the Invention
The present invention relates to devices for cranes and aerial work platforms; and more particularly, to an anti-two block device for cranes and aerial work platforms using non-contact measuring and detecting devices.
2. Description of Related Art
Conventional anti-two block devices rely on physical contact between elements of the device to detect when anti-two block is imminent. Devices which rely on contact, however, have a limited life span because each physical contact serves to wear and degrade the device. Contact devices also fail because of external factors which prohibit the detection of contact. For instance, most contact devices use electrical switches, and freezing rain can prevent such switches from functioning. Furthermore, most contact devices only provide a discreet measurement. When contact occurs, this contact indicates that, for example, anti-two blocking is imminent. Such contact devices cannot supply a continuously varying real-time measurement. Contact devices also have slow response times. Accordingly, contact devices include a certain amount of error.
The anti-two block device according to the present invention includes a non-contact measuring device which detects in one form or another the distance of a load-bearing member from the nose of a boom. By comparing the detection results to one or more predetermined threshold values, the anti-two block device according to the present invention can assist an operator in preventing anti-two blocking in various ways.
For instance, when the distance measured by the non-contact measuring device indicates a distance between the boom nose and the load-bearing members is less than a first predetermined threshold, a warning light is driven and/or the movement of the load-bearing member is slowed. If the measured distance falls below a second predetermined threshold, then movement of the load-bearing member is stopped completely.
The present invention contemplates the use of numerous different non-contact measuring devices such as micro-impulse radar, a sonic measuring device, an ultrasonic measuring, an infra-red measuring device, and a laser measuring device.
Other objects, features, and characteristics of the present invention; methods, operation, and functions of the related elements of the structure; combination of parts; and economies of manufacture will become apparent from the following detailed description of the preferred embodiments and accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures.